1. Field of the Invention
The present invention relates to a photosensing device and a photosensing apparatus, more particularly to a photosensing device and a photosensing apparatus applicable to photon counting, light intensity distribution measurement, or applicable to a color-image pickup element.
2. Related Background Art
In a metal-insulator-metal (MIM) junction, electrons penetrate through the energy barrier in an extremely short time on an order of 10.sup.-16 second. Thus, by use of this type of junction, ultrahigh speed detection of electro-magnetic waves can be achieved over a wide range of frequency from a micro-wave to a visible light. Conventional metal-metal point-contact diodes used for a wave detection and a frequency mixing at far infrared and infrared wavelength regions are, however, weak for a mechanical or electrical shock, resulting in a shorter life because of the point-contact type thereof. (See Koichi IJICHI, and Sogo OKAMURA: Denshi Tsushin Gakkai (Electronic Communication Society), Microwave Research Data: MW-73-27 (1973-06)).
For this reason, a mechanically strong MIM junction is demanded for a practical wave detector. In view of the RC time constant, the resistance for a tunnel current is so very small, that the detected signal cannot be taken out effectively, because the impedance is too low, even in the MIM junction having the minimum area producible by vapor deposition.
On the other hand, a method is considered which utilizes an ultra-thin metal film having an island-like structure prepared by vapor deposition for the purpose of realizing a junction having a minute area. (See T.E. Hartman: J. Appl. Phys., 34, 943 (1963)).
This ultra-thin film has a structure in which numberless MIM junctions are connected mutually in parallel and in series over all the surface. This ultra-thin film is utilized as an ultrahigh speed detector, in which the signals detected by the individual MIM junctions are integrated on the whole surface, and taken out when an infrared light is irradiated on it. However, it is not easy to produce such an ultra-thin metal film having the island-like structure stably and well in repeatability, so that it is difficult to produce elements having constant wave-detection characteristics. Moreover, the ultra-thin film is weak for electric shock and has short life, not necessarily giving a practical element.